Potentiometer



S. R. HUARD April 10, 1962 POTENTIOMETER 4 Sheets-Sheet 1 Filed Feb. 5, 1960 NdI STEPHEN R. HUARD INVENTOR.

ATTORNEYS.

S. R. HUARD POTENTIOMETER April 10, 1962 4 Sheets-Sheet 2 Filed Feb. 5, 1960 STEPHEN R.HUARD INVENTOR.

ATTORNEYS.

A ril 10, 1962 s. R. HUARD v 3,029,404

POTENTIOMETER Filed Feb. 5, 1960 4 Sheets-Sheet 3 ATTOR NEYS.

S- R. HUARD POTENTIOMETER April 10, 1962 4 Sheets-Sheet 4 Filed Feb. 5, 1960 I I08 H I08!) I28 I02 HO 5 |4 IOSc FIG. H.

FIG. l2-

STEPHEN R. HUARD INV EN TOR.

ATTORNEYS.

States 3,029,404 POTENTIOMETER Stephen R. Huard, 133 N. Brightview Drive, Covina, Calif. Filed Feb. 5,1960, Ser. No. 6,917 27 Claims. (Cl. 338-183) Unite tion, sensitivity, and versatility, and which is at the same time rugged and durable.

According to the invention, the potentiometer comprises according to one embodiment thereof, a tubular slide on which is mounted along the length thereof a resistance element and a conductor. The resistance element and conductor are spaced from each other and positioned parallel to each other along the slide. In one preferred form of the invention, the resistanceelement and conductor are positioned parallel to the axis of the slide. If desired, a plurality of sets of such resistance element and its associated conductor, can be positioned along the surface of the slide, each such set being displaced arcuately around the surface of the slide. The slide is non-conductive, or if conductive, has a non-com ductive coating, serving as insulation between the resistance element and the conductor. Thus, for example an aluminum slide can be provided with a hard anodic film on the surface of the slide, serving as insulation between the resistance element and the conductor.

The resistance element is preferably in the form of a coil of resistance wire helically wound with high precision on an electrically insulated conductive mandrel of accurate diametral dimension. To attain precise linear electrical output, the resistance turns of the coil must be spaced or pitched equally; for non-linear function they may be spaced unequally. One form of resistance element of this type commonly employed is known as a violin string winding.

A sliding contact unit is provided which touches each turn of the resistance coil progressively as the sliding contact moves along the axis of the coil, and conductively bridges the resistance coil and its associated parallel conductor. Such unit is in the form of a slidable carrier formed of non-conductive material such as plastic, mounted snugly around the tubular slide and arranged for slidable axial motion along the slide. Positioned on the carrier is a conductive mount having suspended therefrom a pair of brushes, one of which is arranged to contact the resistance coil, while the-other brush contacts the associated conductor as the brush carrier is moved axially along the tubular slide. The interior surface of the brush carrier is offset, or spaced, from the outer surface of the slide so as to provide a space between such interior surface and the resistance element and conductor to permit freedom of motion of the carrierover the resistance'element and conductor. The brushes are so arranged that they will deflect andmaintain firm contact at all points in their travel along the axis of theresistance element and along the axis of the conductor respectively. One such brush mount assemblycomprising a pair of brushes is provided for each additional resistance element and conductor which may be mounted on the slide.

By provision of the structure described above, current passing through the resistance element is reduced by its passage through each turn of the winding, and the sliding contact or brush in engagement therewith will sense and transmit to the conductor, via the brush mount and the other brush in contact with the conductor, the variations a tent 3,029,404 Patented Apr. 10, 1962 in resistance generated by each successive turn of resistance wire.

As additional features of the invention, all electrical leads are connected to fixed elements, that is, to the mandrel on which the resistance Winding is mounted, to the resistance winding itself, and to the conductor, and preferably all leads terminate at the same end of the instrument. Thus, since the core of the mandrel is conductive and is insulated from the coil, the resistance coil may be electrically connected to the core at its far end, to permit travel of current through the coil and the core on which it is wound without the use of an external bus bar. This permits connection of one electrical leadto the core and another electrical lead to the coil at the same end of the instrument to complete the circuit through the resistance coil, and the slider output is connected to an external circuit via the conductor and an electrical lead connected to the end of the conductor adjacent that end of the core and of the coil to which their associated leads are connected. Thus, it is seen that all three leads are connected to the unit at the same end thereof.

The resistance element can be mounted in any desired manner along the surface of the slide. Thus, the resistance element can be positioned in a deep groove provided in the surface of the slide, so that the resistance element is positioned below the outer surface of the slide. Under these conditions the brush can be positioned so that it rides in such groove in contact with the resistance element and the carrier need not be offset or spaced from the surface of the slide adjacent the resistance element. Further, instead of positioning the resistance element in a groove provided in the surface of the tubular slide, the slide may be flattened on one side and the resistance element mounted along the surface of such flat slide and connected thereto by any desired means such as cement,

and the like. In this modification the inner surface of the carrier is spaced from the outer surface of the slide adjacent the resistance element, to permit sufiicient clearance for slidable motion of the carrier on the slide.

Also, the conductor likewise can be mounted in any desired manner along the surface of the slide, either in a groove in such surface, or attached to a flattened portion of the slide as described above with respect to the resistance element. Further, the conductor can be completely omitted from the slide, and the output current taken off by a pigtai type winding loosely wound about the slide and connecting the brush on the carrier in contact with the resistance element, with a terminal at one end of the instrument. This pigtail type lead permits axial motion of the carrier without breaking the connection between the carrier and said terminal.

The brush carrier is actuated for translatory motion on the tubular slide by means of an independently mounted plunger which is coupled by a connecting pin to the carrier. The plunger is mounted in a bearing at one end of the potentiometer and is received within thev tubular slide, preferably closely fitting the inside diameter of the slide. The plunger extends externally of the instrument, and by application of an axial force to the external end of the plunger, the latter can be reciprocated axially relative to the tubular slide, together with the brush carrier, which is coupled to the plunger in the following manner. An annular groove is provided in the plunger adjacent its internal end. A pair of aligned chordal holes are provided in the brush carrier perpendicular to the axis of the slide, and these holes are aligned with a pair of slots extending axially along opposite sides of the slot. The connecting pin is positioned perpendicular to the axis and is received within such chordal holes of the brush carrier and engages the wall of the annular groove of the plunger, preferably in each case by an interference fit, While passing freely through the axial slots in the tubular slide. The above described structure for reciprocal actuation of the brush. carrier is also a structural feature of the invention.

The stability obtained by the mounting of the brush carrier snugly around the slide so that the carrier is well supported on the slide, aids in limiting axial motion of the carrier which may be generated as result of any gyration of the plunger within the slide due to clearance of the plunger with its bearing, on application of an eccentric load or a combined radial and axial load to the outerend of the plunger. This feature effectively eliminates from the system any mechanical hysteresis at the point of brush contact with the resistance coil. Greater control of radial or gyrating plunger motion can be obtained by designing the plunger so that it is closely fitted to the inside diameter of the slide. Such mounting will establish the coupling point as the vertex of the cone of plunger gyration permitted by the clearance between the plunger and the inside diameter of the slide, which in this instance effectively functions as the plunger bearing.

According to a modified form of the invention device, greater resistance and/or resolution, without increasing plunger stroke can be obtained by cutting oppositely aligned helical slots in the tubular slide for receiving the coupling pin which couples the plunger and the brush carrier in the manner described above. The resistance element and the conductor are also formed into a corresponding helix so that the slots in the'slide and the resistance coil and conductor mounted thereon are parallel. As the plunger is actuated the coupling pin will follow the helix formed by the guide slots in the slide, causing the brush carrierto guide its brushes helically along the axes of the resistance element and the conductor, respectively. I

In another modified form of the invention, a combined coarse and fine adjustment of the brush with respect to the associated resistance element can be obtained. This is accomplished according to one embodiment by replacing the plunger with an elongated member having a threaded portion which carries a nut having a transverse hole which clears the outside diameter of the screw threads. The above noted coupling pin passes through this hole in the nut and is received in the brush carrier by interference fit, but is freely received in the slots in the slide, permitting axial or helical motion of the carrier along the tubular slide, as the case may be, when the shaft is rotated with respect to the nut. The shaft normally can be reciprocated axially of the slide to provide a coarse adjustment of the resistance. When a fine adjustment is desired, means is provided to maintain the shaft fixed against axial or translatory motion, but permitting rotary motion of the shaft. Such rotary motion of the shaft causes the nut and the brush carrier coupled therewith to advance in one direction or the other at a slow rat-e of axial displacement along the tubular slide.

According to another modification, the invention device can be in the form of a trimming potentiometer in which the brush carrier is actuated by rotation only of a lead screw, such screw being fixed against axial motion.

The invention will be understood more clearly by reference to the description below of certain specific embodiments, taken in connection with the accompanying drawings wherein:

FIG. 1 is a section shown partly in elevation, through a preferred embodiment of the invention;

FIG. 2 is a plan view of a detail of the potentiometer, showing the wire connections;

FIG. 3 is an enlarged sectional view similar to FIG. 1, but showing the plunger and brush carrier in another position;

FIG. 4 is a section taken on line 4-4 of FIG. 3;

FIG. 5 is a section taken on line 5-5 of FIG. 3;

FIG. 11 is a sectional view of another modified form I of the invention; and V FIG. 12 is a section taken on line 12--12 of FIG. 11.

Referring to FIGS. 1 to 6 of the drawings the potentiometer has mounted axially therein a cylindrical tubular slide 11 on which is mounted a resistance element 12 and a conductor 13. In this particular embodiment, the slide 11 is constructed of aluminum and has on the surface thereof a hard anodic coating 16 forming insulation thereon. The resistance element 12 and the conductor 13 are spaced a short distance from each other on the surface of the tubular slide and extend parallel to each other and parallel to the axis of the tubular slide, the resistance element 12 and conductor 13 preferably being coextensive in length. The resistance element 12 is positioned in a groove 14 of semicircular shape extending along the surface of the tubularslide and the conductor 13 is positioned in a groove 15 extending along the surface of slide 11 parallel to groove 14. The resistance element 12 and conductor 13 may be fixedly positioned in their respective grooves 15 and 14 by press fit or by any other suitablemeans. 7

Resistance element 12 is preferably formed of a copper mandrel 18 which is insulated along the surface, for example, by a non-conductive varnish, and a coil of resistance wire 17 wound about the copper mandrel. Preferably the resistance coil is in the form of a so-called violin string winding consisting of a large number of resistance wires helically wound with high precision on the electrically insulated copper mandrel. The conductor 13 is in the form of a conductive metal bar, e.g. formed of palladium or other precious metals. The resistance element 12 and conductor 13 are insulated from the tubular slide 11 by the anodic coating 16 on the surface of slide 11. To insure better insulation for this purpose, that portion of the conductor 13 in contact with the slide 11 can be coated with a nonconductive varnish. An electrical lead 19 (see FIG. 2) is connected to one end of the copper mandrel 18, and an electrical connection 20 is provided between the copper mandrel 18 and the resistance coil 17 at the far end of the copper mandrel. An electrical lead 21 is connected to the resistance coil 17 at the end thereof adjacent the end of the copper mandrel to which the lead 19 is connected. Another lead 22 is connected to the conductor 13 adjacent the ends of the copper mandrel 18 and the resistance coil 17 to which the leads 19 and 21 are connected. It is thus seen that all of the electrical leads 19, Hand 22 are connected to terminals at one end of the instrument. The electrical leads 19, 21 and 22 pass through a terminal flange 23 and through a cap 25 mounted at one end of the instrument and the leads are then brought out of the instrument through a cable 26 for external connection to the desired circuit. Leads and/or terminals 19, 21 and 22 are preferably sealed by the application between their outer periphery and the inside diameters of the holes thru which they pass of a plastic potting compound or bonding agent. By so filling the space left between the leads and the holes in the terminal flange, the entrance of liquid, solid or gaseous contaminants from the outside to the interior of the potentiometer Will be prevented.

In'the embodiment shown in FIGS. 1 to 6 there are two units composed of the resistance element 12 and tubular slide 11 together with two sets of the leads and associated connections described above. In this manner a plurality of, in this case two, external circuits can be controlled by the potentiometer of the invention, The

5 second unit comprising resistance element and conductor shown in FIGS. 1 to 6 of the drawing is mounted diametrically opposite the first unit described above and the second elements of this unit are designated by primed numbers corresponding to the elementsdesignated by unprimed numbers described above.

A slidable contact unit 30 is disposed around the outer surface of the tubular slide 11. This unit 30 comprises a slidable ring shaped carrier 31 whose inner diameter along a substantial portion thereof indicated at 31a in FIG. 4 is in snug engagement with the outer surface of the tubular slide 11 but is slidable axially along slide 11.

It will be further noted that the slidable carrier 31 has a substantial lengthwise dimension axially of the slide 11 so that the ring shaped member 31 is firmly supported on the surface of the slide against oscillatory motion axially of the slide. The slidable carrier 31 is formed of a non-conductive material such as plastic. A conductive brush mount 32 is connected'to the slidable carrier 31 by means of screws 33. Suspended from the brush mount 32 are a pair of conductive brushes 34 and 35 which are spaced from each other a distance equal to the distance between the axis of the resistance element 12 and the axis of the conductor 13. Brushes 34 and 35 are formed of resilient spring material and the brushes are so mounted on the carrier 31 (see FIG. 3) that the lower end 34a of brush 34 is in tight engagement with the resistance coil 17 of resistance element 12 and the end 35a of brush 35 is in tight engagement with the bar forming conductor 13. In this manner brushes 34 and 35 are maintained in firm contact at all'points in their travel along the axis of the resistance element 12 and the axis of the conductor 13. In the construction shown, brushes 34 and 35 have their free ends 34a and 35a, respectively, positioned beneath the inner surface 31b of the forward portion 29 of brush carrier 31.

A separate brush mount assembly and pair of brushes similar to 34 and 35 are provided for each additional resistance element and each conductor mounted on the tubular slide 11. p

It is noted in FIGS. 3 to 5 that the inner surfaces 31a and 31b of slidable carrier 31 are offset or spaced from the outer surface of slide 11 and from the resistance elements 12 and 12' and from the conductors 13 and 13' to permit axial motion of the carrier over the slide without interference from the resistance elements and conductors projecting from the outer surface of the slide.

It is thus seen that current traversing resistance element 12 passes through the circuit including electrical lead 19, mandrel 18, connection 20, the resistance coil 17, and lead 21. The slider output obtained by passage of current from the resistance coil 17, through brush 34,

. conductive brush mount 32, brush 35 and the conductor 13 is taken off via electrical lead 22. As the slidable carrier 31 is moved axially along the tubular slide 11 the brush 34 moves to successive turns of the resistance coil 17, varying the resistance in the 'coil which is sensed and transmitted by the brush 34 to the conductor 13.

In the embodiments shown in FIGS. 1 to 6' one additional such brush mount unit 30' is shown mounted diagonally opposite brush mount 30, and whose structural elements including brushes 34 and 35' are indicated by primed numbers corresponding to the same structural elements of the brush mount 30 described above.

The slidable carrier 31 is reciprocated axially along the tubular slide 11 by means of a plunger 39 which is mounted in a bearing 46 positioned in a bearing flange 41 at the outer end of the potentiometer. The bearing flange 41 carries screw thread 42 for engagement with screw threads of a body member in which the potentiometer is to be positioned. The plunger 39' has an external- 1y extending portion 49 and an internally positioned portion 43 axially mounted within slide 11. By application of an axial forceto the externally located portion 49 of the plunger the plunger can be reciprocated axially with tion potentiometer.

I parallel thereto along the surface of the slide 60.

6. respect to the tubular slide 11. The terminal flange 23 carries an O-ring 24 and the bearing flange 41 carries an O-ring 44-. A case 10 can be slid over the O-rings 24 and 44 of the flanges 23 and 41 with one end of the case abutting a shoulder formed on the peripheral edge of the cap 25.

The bearing 40 in which the plunger 39 is mounted is of substantial length and holds the plunger at all positions thereof along the axis of slide 11, and prevents any substantial gyrating or radial motion of the inner end of the plunger 39. Preferably, however, the inner portion 43 0f the plunger 39 has an outer diameter which is almost as great as the inside diameter of the slide 11 within which portion 43 is mounted, so that the inner wall of slide 11 in effect functions as a bearing for portion 43 to prevent such aforementioned gyratory motion of the inner portion 43 of the plunger. An annular groove 47 is cut in the plunger 39 adjacent the inner end thereof for a purpose which will be made clear below. A stop screw 48 is mounted in the cap 25 and is adjustable for limiting the motion of the plunger 39 in an axial motion to the left as viewed in FIG. 1.

A pair of aligned chordal holes 53, see FIGS. 4 and 5, are provided in the slidable carrier 31, such holes being positioned perpendicular to the axis of the slide 11, and these holes are aligned with a pair of slots 54 cut'into opposite sides of the tubular slide 11. A connecting pin 52 is received within the chordal holes 53 of carrier 31 and is received within the annular groove '47 of the plunger 39, the pin having an interference fit with the holes 53 in the carrier 31 and with the wall of the groove 47, but being slidably received within the slots 54 of the slide. Thus it will be seen that on axial motion of the plunger 39 the connecting pin 52 will be carried axially with the plunger in turn causing axial movement of the brush carrier 31 and the brushes 34, 35 and 34', 35' mounted thereon.

It is noted that the brush carrier 31 mounted snugly on the tubular slide 11 and firmly supported thereon, together with the bearing 40 provided for the plunger 39 and/or the closefitting between the inner portion 43 of the plunger and the internal wall of the slide 11, cooperate to greatly limit any axial motion of the'brush carrier 31 which may be produced as result of any gyration of the plunger within the slide about the apex of the cone of gyration within bearing 40, as result of an eccentric load which may be applied to the outer end of the plunger 39.

In FIG. 7 there is shown a modified form of'the inven- According to this modification the tubular slide has therein a pair of helical slots 63 formed on opposite sides of the slide. These helical slots are positioned parallel to each other and extend about 90? about the surface of the slide from one end 64 of the slide to the opposite end thereof. The resistance element 61 formed in the same manner as resistance element 12 is positioned on the slide 60 in a helical groove 64 therein so that the resistance element 61 extends in a helix of the same shape as the helical slots 63 and In the same manner the conductor 62 is formed in a helix parallel to the helical resistance element 61 and the helical slots 63, conductor 62 being positioned in a helical groove 65' in slide 60. It will thus be seen that as the plunger 39 is moved axially it Will carry the connecting pin 52 along with it, and since the pin 52 will slide within the helical slots 63 the pin will be rotated accordingly during its travel along the helical slots 63 and at the same time the brushes 34 and 35 will travel in a'similar helical path in contact with the helical resistance element 61 and the helical conductor 62. Since for the same length of tubular slide 60 the length of resistance element 61 will be greater than the length of the, resistance element 12 in the device of FIGS. 1 to 6, a greater amount of plunger stroke will be required to produce a corresponding displacement of the brush 34 in contact with the resistance element 61. The result is an instrument having greater resistance and/ or resolution without increasing plunger stroke as compared to the potentiometer of FIGS. 1 to 6 having a resistance element which runs parallel to the axis of the tubular slide 11.

In FIGS. 8 to 10 is shown another modification of the potentiometer which provides for both a combined coarse and fine adjustment of the contact brush 34 with its associated resistance element. In this embodiment, a case 67 is threadably mounted on end flanges 68 and 69. A tubular slide 70 is threadably supported at one end on a hub 70 of the flange 68 and at the other end is supported by insertion of a shoulder 70a of the slide within a recess 7% of the flange 69. In a manner similar to that described above with respect to the device of FIGS.'1 to 6 a brush carrier 71 in the form of a ring shaped element is snugly positioned about the slide 70 and arranged for axial motion along the slide. The carrier has mounted thereon a conductive brush mount 72 and brushes 73 and 74 which are spaced apart. Brushes 73 and 74 are defiected,with the outer ends thereof respectively in contact with a resistance element 75 like 12, positioned axially along the surface of the slide in the same manner that the resistance element 12 is positioned along the slide 11 in the device of FIGS. 1 to 6, and the end of brush 74 is likewise deflected and maintained in contact with a conductor 76 similar to the conductor 13 in the device of FIGS. 1 to 6. Resistance element 75 and conductor 76 are spaced from each other and insulated from each other and from tubular slide 70 by provision of an anodic coating on slide 70, in a manner similar to that described above for slide 11, and 75 and 76' extend parallel to each other and to the axis of the tubular slide 70.

Mounted within a bearing 89 supported within the flange 68 is the outer end of a shaft 77 which is mounted axially with respect to the tubular slide 70. Within the tubular slide 70 shaft 77 has a threaded portion 78 on which is mounted a nut 79. A connecting pin 80 is mounted in oppositely aligned holes 81 in the brush carrier 71 by an interference fit, the pin passing through a hole 80' in the nut 79, such hole 80' being in alignment with the holes 81 and with a pair of oppositely positioned slots 82 in the slide 70. The pin 80 is received for 1 slidable movement within the slots 82.

The shaft 77 has a portion 90 which extends outwardly beyond the flange 69 through an aperture 91 in the flange 92 of the slide 70 and an aperture 93 in the flange 69. The portion 90 of shaft 77 is square shaped as indicated at 88 in FIG. 9. On portion 90 of shaft 77 is mounted a collar 83, the square portion 88 of the shaft being slidable axially with respect to the collar 83. Mounted in the cap portion 94 of flange 69 is an adjustable screw 85 in contact at its inner end with a ball bearing 86 which rides in a groove 95 formed in the outer periphery of collar 83. Shaft 77 has a groove 96 at its external end for rotation by a tool inserted in said groove.

In the operation of the device of FIGS. 8 to 10, if it is desired simply to employ the coarse adjustment for axial displacement of the shaft 77 so as to obtain relatively large movement of the brush 73 on the resistance element 75, the screw 85 is backed off so that there is no binding force exerted by the collar 83 against the shaft 77. This permits axial displacement of shaft 77 thereby carrying nut 79 and the pin 80 in a corresponding axial displacement together with the carrier 71 and the brushes 73 and 74.

If at any time it is desired to obtain a fine adjustment of the brush 73 with respect to the resistance element 75, then the nut 85 is tightened against the ball bearing 86 to urge the collar 83 in an upward direction as viewed in FIG. 8 to produce a binding effect of the collar against the square portion of the shaft. This binding other, due to reaction thereon of thethreaded portion 78 of the shaft. Such axial displacement of the nut 79 however will be of a minor nature with respect to the amount of rotation imparted to the shaft 77. Such minor displacement of nut 79 axially along the slide 70 will produce a corresponding minor displacement of the connecting pin and hence of the carrier 71 and brushes 73 and 74. The result will be a minor variation in the resistance for a given amount of rotation of the shaft 77.

The modification shown in FIGS. 11 and 12 is a socalled trimming potentiometer, that is, one in which the brush carrier is actuated by rotation only of the shaft as a lead screw. Further, in this embodiment" the conductor to which the output current is passed, is not mounted on the tubular slide, but is taken directly off the brush carrier by a pigtail connected to the brush carrier and to the opposite end of the instrument. In the drawing, end flanges 100 and 101 have mounted thereon the case 102. Positioned on inner hubs 103 and 104 of these end flanges is a tubular slide 105 formed of a non-conductive material such as plastic, the slide having longitudinally extending aligned slots 106 of equal length provided in opposite sides of the slide offset from the axis of the slide. The slide 105 is flattened at 107 on one side thereof, and a resistance element 108 formed of a conductive core 109 and a resistance coil 110 insulated from each other, is positioned centrally on the flattened surface 107 and extends along the slide parallel to the axis thereof. The resistance element 108 is attached to surface 107 by any suitable means such as a cement.

Diametrically opposite resistance element 108, there 7 is provided in the slide 105 a deep groove 111 extending parallel to the axis of the slide and to resistance element 108. In groove 111 is positioned a second resistance element 108 of a construction the, same as 108. It will be noted that resistance element 108' extends inwardly from the adjacent outer surface 112 of the slide 105. Leads 108a and 1081) are connected to core 109 and coil 110, respectively, and pass through end flange 101 for connection to an external circuit, and leads 108a and 108b' are connected to core 109" and coil 110; respectively, of resistance element 108, and pass externally through end flange 101. An electrical connection 1108c is made between core 109 and coil 110 at the opposite end of resistance element 108, and an electrical connection 1080' is made between core 109 and coil 110' at the opposite end of resistance element 108.

Mounted snugly about and in slidable relation on slide 105 is a ring shaped brush carrier 113. It will be noted that an arcuate portion 114 of the inner periphery of slide 113 is spaced from the flattened surface 107 of the slide 105. Also a portion 115 of the inner surface of the carrier 113 diametrically opposite portion 114 slides over the groove 111 and spaced from the resistance element 108 positioned in such groove.

The brush carrier 113, formed of a non-conductive material carries a conductive bolt 116 adjacent its outer periphery parallel to the axis of the slide, and to one end of the bolt is connected a brush 117 formed of a resilient, material. The brush 117 is deflected so that the free end thereof frictionally engages the resistance element 108 and is maintainedin tight but slidable contact with such element as the carrier 113 is moved over the slide 105 in the manner describedbelow. The opposite end of bolt 116 has connected thereto a pigtail lead 118 which 9 is wound loosely about the slide 105 and over the resistance element 108, as seen in H6. 11, and is connected at its opposite end to a lead 119 passing through the end flange 101.

In brush carrier 113 diagonally opposite bolt 116' is another conductive bolt 125 passing through the carrier parallel to the axis of the slide. To one end of bolt 125 is connected a brush 126 which extends into the groove 111 of the slide and makes a firm sliding contact with resistance element 108 as result of deflection'of the brush 125 against the resistance element. A pigtail lead 127 is connected to the opposite end of bolt 125 and is wound about slide 105 and resistance element 108, and is connected at its opposite end to a lead 128 which passes externally through end flange 101, both pigtails 118 and 127 being wound in the form of a double helix about the slide 105.

Mounted within a bearing 130 is the outer end of a lead screw 131 mounted axially with respect to tubular slide 105, the opposite end of the lead screw beingjournaled in bearing 132 provided in end flange 101. The lead screw 131 carries collars 133 and 134 which abut the inner surfaces of end flanges 100 and 101, respectively to prevent axial motion of the lead screw. Between collars 133 and 134 the lead screw is threaded at 135 for a distance somewhat greater than the length of slots 106 in slide 105. On the threaded portion of lead screw 131 is mounted a nut 136. A connecting pin 137 is positioned in oppositely aligned holes 138 of the brush carrier 113 by an interference fit and passes through a hole 139 in the nut 136, said hole being aligned with holes 138 of the carrier 113 and with the slots 106 in slide 105, the pin 137 being received for slidable movement in slots 106. The end of the lead screw 131 has a groove 140 therein for engagement by a tool for rotation of the lead screw.

It will be seen that rotation of the lead screw 113 in one direction will produce axial displacement of the nut 136 in one direction causing a corresponding displacement of the brushes 117 and 126 with respect to their associated resistance elements 108 and-108, to change the outputs of the respective circuits. Rotation of the end of screw 131 in the opposite direction'will produce axial displacement of nut 136 and brushes 117 and 126 in the opposite direction. The extremities of displacement of nut 136 are provided by abutment of nut 136 with collar 133 or 134 at'opposite ends of the threaded portion 135 of the lead screw. It will be seen that this embodiment can produce minor variations in resistance by small rotary movements of lead screw 131.

In place of the aluminum slide having an anodic insulation coating on the surface thereof, I can employ a conductive material other than aluminum having a different type of insulation coating thereon, or I can employ as the tubular slide member a non-conductive material such as plastic and thus avoid application of an insulation coating to the surface thereof, to insulate the resistance element, e.g. member 12, from the adjacent conductor, e.g. member 13.

It will be understood that means other than that described and shown can be employed for guiding the brush carrier along the slide, and for coupling the brush carrier with the plunger for axial motion of the brush carrier along the slide.

Further, alternative types of resistance elements different from that shown and described can be utilized. Thus, for example, by using magnet wireas the core on which the resistance coil is wound, variations in resistance of the coil from sample to sample may be compensated by adjusting the diameter of the core by stretching the core beyond its elastic limit to reduce its diameter. This adjustment permits accuracy beyond machining possibilities.

With respect to the embodiment of FIGS. 8 to 10, any means other than that shown and described can be employed to lock the shaft against axial displacement while permitting rotation of the shaft, so as to cause axial motion 10 of the nut 79 and corresponding motion of the brush carrier to obtain the fine adjustment of the brush with respect to the resistance element.

While I have described particular embodiments of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. A potentiometer which comprises a fixed tubular slide, a resistance element mounted on and extending along the outer surface of said slide, said resistance element being electrically insulated from said slide, movable means mounted exteriorly of said slide for movement axially of said slide, a conductive contact means on said movable means electrically contacting said resistance element at a localized portion thereof, output conductor means electrically connected to said contact means, means for guiding said movable means along said tubular slide with said contact means in continuous contact with said resistance element, means for moving said movable means axially of said slide, said contact means moving in a substantially axial path and engaging successive localized portions of said resistance element during such motion of said movable means, and an electrical connection to said resistance element and an electrical connection to said conductor means.

2. A potentiometer as defined in claim 1, said resistance element comprising a conductive core having a resistance wire wound thereon, said resistance wire and said core being insulated from each other.

3. A potentiometer as defined in claim 2, said core being conductive, said resistance wire and said core being insulated from each other, an electrical connection at one end of said core, an electrical connection at one end of said resistance wire adjacent said one end of said core, said resistance wire and said core being electrically connected at their adjacent other ends, and an electrical connection at one end of said conductor means adjacent said one end of said core and said one end of said resistance wire.

4. A potentiometer which comprises a fixed tubular slide, a resistance element mounted on and extending along the outer surface of said slide, a conductor mounted on and extending along the outer surface of said slide, said conductor being spaced from said resistance element and positioned substantially parallel thereto, said conductor and resistance element being electrically insulated from each other and from said slide, movable means mounted on said slide and movable axially of said slide, a first conductive con-tact means on said movable means electrically contacting said resistance element at a localized portion thereof, a second conductive contact means on said movable means electrically contacting said conductor, said first and second contact means being electrically connected, means for guiding said movable means along said tubular slide with said first and second contact means in continuous contact with said resistance element and said conductor respectively, means received within said tubular slide for moving said movable means axially of said slide, said first contact means engaging successive localized portions of said resistance element during axial motion of said movable means, and an electrical connection to said resistance element and an electrical connection to said conductor.

5. A potentiometer as defined in claim 4, said resistance element comprising a core having a resistance wire wound thereon, and said conductor comprising a conduct-ive bar, said slide having a first groove and a second groove, said grooves being parallel, said resistance element being mounted in said first groove and said conductor being mounted in said second groove.

6. A potentiometer as defined in claim 4, wherein said resistance element and said conductor each extend along the outer surface of said slide parallel to the axis thereof.

7. 'A potentiometer as defined in claim 4, said movable means comprising a ring shaped member tightly fitted around the outer surface of said slide but slidable thereon over said resistance element and said conductor, said first and second contact means comprising a'first resilient conductive brush and a second resilient conductive brush, a conductive brush mount connected to said ring shaped member, said brushes being mounted in spaced relation on said brush mount, said first brush being deflected against and maintained in tight but slidable contact with said resistance element, and said second brush being deflected against and maintained in tight but slidable contact with said conductor.

8. A potentiometer as defined in claim 1, wherein said output conductor means is in the form of a wire wound helically about said slide and over said resistance element, said wire being connected at one end to said contact means.

9. A potentiometer as defined in claim 1, wherein said slide is composed of aluminum, said slide having an anodic film on the outer surface thereof, said film forming insulation between said resistance element and said slide.

10. A potentiometer as defined in claim 1, wherein said resistance element extends in the form of a helix along the outer surface of said slide, and said conductor is in.

the form of a conductive bar extending in the form of a helix along the outer surface of said slide, said helixes being parallel to each other.

111 A potentiometer as defined in claim 1, said movable means comprising a ring shaped member tightly fitted around the outer surface of said slide but slidable thereon over said resistance element, said contact mean-s comprising a conductive brush mounted on said ring shaped member.

12. A potentiometer as defined in claim 1, said means for guiding said movable means comprising a pair of oppositely positioned aligned slots disposed along the surface of said slide, a pin connected to said movable means and received for slidable movement in said slots, and means connecting said pin with said means for moving said movable means along said slide.

13. A potentiometer as defined in claim 1, said means for moving said movable means including means for coarse adjustment and means for fine adjustment of the amount of axial displacement of said movable means and said contact means with respect to said resistance element, and means for inactivating said coarse adjustment means and permitting actuation of said fine adjustment means.

14. A potentiometer as defined in claim 11, said means for guiding said ring shaped member comprising a pair of oppositely positioned aligned slots disposed along the surface of said slide, a pin connected to said ring shaped member and received for slidable movement in said slots, and means connecting said pin with said means for moving said ring shaped member along said slide.

15. A potentiometer as defined in claim 12, said moving means comprising a plunger mounted on the axis of said tubular slide, a bearing at one end of said potentiometer for receiving said plunger to permit axial motion of said plunger, the outer end of said plunger extending externally of said potentiometer, the inner end of said plunger being received within said tubular slide, said plunger being mounted in said bearing for minimum radial displacement of the inner end of said plunger with respect to said slide on application of an eccentric force at the outer end of said plunger, an annular groove in said plunger adjacent the inner end thereof, said connecting pin being received in said annular groove in tight frictional engagement with the wall of said annular groove, said plunger on axial motion thereof carrying said pin and causing corresponding axial motion of said movable means.

16. A potentiometer as defined in claim 12, said moving means comprising a shaft mounted on the axis of said tubular slide, a hearing at one end of said potentiometer for receiving said shaft to permit axial and rotary motion of said shaft, the outer end of said shaft extending externally of said potentiometer, the inner end of said shaft being received Within said tubular slide, said shaft having a threaded portion within said slide, a nut mounted on said threaded portion of said shaft, said connecting pin passing transversely through said nut, and means cooperating with said shaft for locking said shaft against axial motion, but permitting rotary motion of said shaft, to permit said screw to advance axially on the'threaded portion of said shaft, causing a corresponding axial motion of said movable means.

17. A potentiometer as defined in claim 12, said moving means comprising a shaft mounted on the axis of and positioned within said tubular slide, bearings at opposite ends of said potentiometer for receiving said shaft to permit rotary motion of said shaft, means preventing axial motion of said shaft in said bearings, one end of said shaft extending externally of said potentiometer, said shaft being threaded within said slide, a nut mounted on said threaded portion of said shaft, said connecting pin passing transversely through said nut, whereby on rotation of said shaft, said screw advances axially on the threaded portion of said said shaft, causing a corresponding axial mot-ion of said movable means.

18. A potentiometer as defined inclaim 12, said moving means comprising a shaft mounted on the axis of and Within said tubular slide, means for receiving said shaft to permit slidable motion of said shaft within said slide, one end of said shaft extending externally of said potentiometer, and an annular groove in said shaft, said connecting pin being received in said annular groove in tight frictional engagement with the wall of said annular groove.

19. A potentiometer as defined in claim 15,. wherein the diameter of said plunger within said slide is slightly less than the inside diameter of said slide.

20. A potentiometer as defined in claim 16, wherein said means cooperating with said shaft comprises a collar mounted on said shaft, said shaft being slidable axially with respect to said collar, means keying said collar to said shaft for rotation therewith, means for urging said collar into tight frictional engagement with said shaft 'to prevent axial motion of said shaft with respect to said collar, while permitting rotary motion of said collar and said shaft.

' 21. A potentiometer which comprises a case, a cylindrical tubular slide fixedly mounted axially within said case, a pair of spaced parallel grooves in the outer surface of said slide and extending along the outer surface thereof parallel to the axis of said slide, a resistance element positioned in one of said grooves, a' conductor positioned in the other of said grooves, said resistance element and conductor being coextensive in length, said resistance element including a core having a resistance wire wound thereon, and said conductor comprising a conductive bar, said core and'said wire being insulated from each other, a pair of oppositely positioned aligned slots in said slide, said slots being parallel to each other andto said resistance element and said conductor, a carrier tightly fitted around the outer surface of said slide but slideable-thereon, the inner surface of said carrier adjacent said resist ance element and said conductor being spaced therefrom to permit axial motion of said carrier on said slide, a conductive brush mount on said carrier, a first resilient conductive brush mounted on said brush mount, a second for receiving said plunger to permit axial and rotary motion of said plunger, the outer end of said plunger extending externally of said potentiometer, the inner end of said plunger being received within said tubular slide, said plunger being mounted in said bearing for minimum radial displacement of the inner end of said plunger on application of an eccentric force at the outer end of said plunger, a pin connected to said plunger and mounted by friction fit in aligned holes in opposite sides of said carrier, said pin received in the slots of said tubular slide for slidable movement in said slots, said plunger on axial motion thereof carrying said pin and causing corresponding axial motion of said carrier and said first brush with respect to said resistance element.

I 22. A potentiometer as defined in claim 21, said core being conductive, an electrical connection at one end of said core, an electrical connection at one end of said resistance wire adjacent said one end of said core, said resistance wire and said core being electrically connected at their adjacent other ends, and an electrical connection at one end of said conductor adjacent said one end of said core and said one end of said resistance wire.

23. A potentiometer as defined in claim 21, wherein said slide is aluminum, said slide having an anodic film on the outer surface thereof, said film forming insulation between said resistance element, said conductor and said slide.

24. A potentiometer as defined in claim 21, wherein the diameter of said plunger within said slide is slightly less than the inside diameter of said slide.

25. A potentiometer which comprises a case, a cylindn'cal tubular slide fixedly mounted axially within said case, a pair of spaced parallel grooves in the outer surface of said slide and extending along the outer surface thereof parallel to the axis of said slide, said grooves being coextensive in length, a resistance element positioned in one of said grooves, a conductor positioned in the other of said grooves, said resistance element and conductor being coextensive in length, said resistance element including a core having a resistance wire wound thereon, and said conductor comprising a conductive bar, said core and said Wire being insulated from each other, a pair of oppositely positioned aligned slots in said slide, said slots being parallel to each other and to said resistance element and said conductor, a ring shaped carrier tightly fitted around the outer surface of said slide but slidable thereon, the inner surface of said carrier adjacent said resistance element and said conductor being spaced therefrom to permit axial motion of said carrier on said slide,

. a conductive brush mount on said carrier, a first resilient conductive brush mounted on said brush mount, a second resilient conductive brush mounted on said brush mount, said brushes being spaced from each other a distance equal to the space between said resistance element and said conductor, said first, brush being deflected against and maintained in tight but slidable contact with said resistance element, and said second brush being deflected against and maintained in tight but slidable contact with said conductor, a plunger mounted on the axisof said tubular slide, a hearing at one end of said potentiometer for receiving said plunger to permit axial motion of said plunger, the outer end of said plunger extending externally of said potentiometer, the inner end of said plunger being received within said tubular slide, said plunger being mounted in said bearing for minimum radial displacement of the inner end of said plunger on application of an eccentric force at the outer end of said plunger, an annular groove in said plunger adjacent the inner end thereof, a pin mounted by friction fit in aligned holes in opposite sides of said carrier, said pin received in the slots of said tubular slide for slidable movement in said slots, and said pin being received in said annular groove in said plunger in tight frictional engagement with the wall of said annular groove, said plunger on axial motion thereof carrying said pin and causing corresponding axial motion of said carrier and said first brush with respect to said resistance element.

26. A potentiometer which comprises a fixed tubular slide, a resistance element mounted on and extending alongthe outer surface of said slide, said resistance element being electrically insulated from said slide, a slidable carrier mounted on said slide and movable axially of said slide, a conductive contact means upon said carrier electricaliy contacting said resistance element at a localized portion thereof, output conductor means electrically connected to said contact means, means for guiding said slidable carrier along said tubular slide with said contact means in continuous contact with said resistance element, plunger means for moving said carrier axially of said slide, said plunger means being received for sliding movement within said tubular slide, means connecting said plunger means and said slidable carrier, said contact means moving in a substantially axial path and engaging successive localized portions of said resistance element during axial motion of said carrier, and an electrical connection to said resistance element and an electrical connection to said conductor means.

27. A potentiometer, as defined in claim 26, said resistance element comprising a core having a resistance wire thereon, said output conductor means comprising a conductive bar mounted on and extending along the outer surface of said tubular slide substantially parallel to said resistance element, said conductive bar being electrically insulated from said slide, and a second contact means on said carrier electrically contacting said conductive bar, said second contact means being electrically connected to said first-mentioned conductive contact means.

References Cited in the file of this patent UNITED STATES PATENTS 2,372,840 Mattern -c Apr. 3, 1945 2,856,493 Blanco Oct. 14, 1958 2,898,568 Bourns et a1 Aug. 4, 1959 2,940,059 Rehnborg June 7, 1960 2,952,827 'Se'mple et a1. Sept. 13, 1960 FOREIGN PATENTS 1,121,451 France Apr. 30, 1956 

